Process of plating aluminium.



No. 64!,709. Patented m. 23, 1900;.

r w. H. LEGATE.

PROCESS 0F PLATHNG ALUMINIUM.

(Application fixed Mar. 10, 1899.) (N0 Madel.)

/ X T X I? f i NrrnD STATES PATENT OFFICE.

WILLIAM H. LEGATE, OF HARTFORD, CONNECTICUT.

PROCESS OF PLATING ALUMINIUM.

SPECIFICATION forming part of Letters Patent No. 641,709, dated January 23, 1 900.

Application filed March 10, 1899. Serial No. 708,574. (No specimens.)

To all whom, it may concern:

Be it known that I, WILLIAM H. LEGATE, a citizen of the UnitedStates of America, residing at Hartford, in the county of Hartford and State of Connecticut, have invented new and useful Improvements in the Process of Plating Aluminium, of which the following is a specification.

This invention relates to the electrodeposition of metals, and particularly to the deposition thereof on the metal aluminium and its alloys, and has for its object the perfection of the process of electroplating aluminium, whereby the deposition of various metals and alloys of metals on metal aluminium may be made permanent and not subject to change after said deposition has been made; and the invention consists in the process of preparing the surface of aluminium for the reception of a metallic amalgam or base on which the aluminium is finally deposited, all as fully described in the following specification, and clearly pointed out in the claims. I

Processes have already been invented for depositing metals on aluminium, but they have been faulty, in that aftera certain time salts form between the surface of the aluminium and the deposited metal, which cause a pitting of the plate and disintegration of the deposited metal. Said salts will force the latter away from the surface of the plate, causing what is in appearance small blisters which are readily broken and, which give to the plated article a rough surface and expose the surface of the aluminium below, whereby oxidation thereof is rendered possible, and hence a further separation of the deposited metal from the aluminium plate. These defects arise from an imperfect cleaning of the surface of the aluminium to be plated, resulting in an imperfect union of the deposited metal and the surface of the article plated.

The known processes of plating aluminium have followed the methods usually employed in preparing metallic surfaces to receive a coating of some other metal-win, by gradually building up a thin metallic coating on said surfaces by the use of what are known as the striking solutions or whiteners and are familiar to those skilled in the art.

Figure 1. of the drawings represents the whitening or striking solutions working on the same current, and Fig. 2 represents a striking solution working on a current of different strength.

In the drawings, P represents the positive and N the negative rods on which the anodes and articles to be plated are respectively hung.

B represents a source of electricity, R the resistance, and T the vats or tubs.

The essential feature of this invention, on the contrary, lies in the process, as hereinafter fully described, for fixing on the surface of the aluminium article to be plated a metallic amalgam,whereby a base is provided on which the striking solution may act with positiveness, the said amalgam base so intimately adhering to the surface of the aluminium that after passing through the striking solutions the metal may be rolled, drawn, or handled in any similar way without causingany separation of the deposited metal film from the surface thereof; and, furthermore, the process to which the aluminium is subjected, as herein set forth, preparatory to the application of the amalgam to the surface thereof is of such a nature as to preclude the forma-' tion of metallic salts at any time after the plating process has been completedbetween the surface of the article and the metal deposited thereon, whereby a separation of the latter from the former may be effected.

The aluminium articles to be plated are first put into boiling whale-oil soap or socalled platers compound for a few moments and are then rinsed in boiling water to remove any of the soapy solution adhering to them. After rinsing in running water they are dipped in a bath of muriatic acid having a gravity of 15 by Baum hydrometer and remain in this bath until some evolution of gas takes place. This dip acts more particularly upon traces of iron and silica lying on the surface of the aluminium, and from this acid-bath .the articles are dipped in hot water to destroy the bubbles left on the surface thereof by the action of the acid-bath. Otherwise the metal would, after plating, show pits in the surface where the bubbles of gas formed on its surface. After proper rinsing the articles are then dipped in a cyanid-of-potassium solution of about 20 gravity by Baum hydrorneter and from thence after rinsing into phosphoric acid of 50 gravity Baum, where it remains from eight to ten minutes. This acid being a solvent for aluminium, its attack upon. the metal removes the greasy surface peculiar thereto and which (together with traces of other metals in the aluminium) has been the great obstacle to perfect union between said metal and metal deposited thereon, which serves ultimately for the base on which the final coating is deposited. It can easily be determined by an experienced man when this greasy surface has all been properly cleansed by the manner in which the solution runs off from the surface of the metal. As soon as it is found in proper condition it is withdrawn from the acid-bath, rinsed, dipped in the cyanid-of-potassium bath again, and finally rinsed, when it is ready for immersion in the amalgamating solution, which is composed of the following ingredients: To one gallon of rain-water as much sal-ammoniac is added as it will take up-say, practically, eight ounces to the quart. To this gallon of solution add one ounce of bichlorid of mercury. Cyanid of mercury may be substituted for the bichlorid, if desired. The solution should have a gravity of 12 by Baum hydrometer and may be tested by dipping a piece of clean copper wire into it in the usual manner and if it whitens the wire it shows it is in working order. The aluminium article to be plated is now dipped as a next step into this amalgamating solution, and after rinsing into a boiling solution of caustic potashwood-potash so calledor any alkaline solution the article may be passed through the amalgamating solution and hot alkaline bath twice, if required, to perfectly coat every part of it.

\Vhen the article is properly amalgamated, it has the same appearance a piece of zinc would have if first cleansed by acid and then dipped in mercury.

When properly amalgamated, the article may be rinsed off and then passed through the striking solutions or whiteners and from thence to the plating solution for final coating with whatever metal may be desired.

It will be observed that the process up to the point of immersing the article in thewhiteners has been directed to preparing it to receive a very thin coating of amalgam and to the application of the latter by dipping in a solution having the requisite properties. Up

.to this point the process differs radically from previous processes in that in the latter efforts have been directed to preparing the surface of the aluminium for the reception of the metal to be deposited thereon by immersing the articles in the whiteners, and thus building up an electrically-deposited base for the reception of the final coating. In this invention that base is provided by the flowing of the entire surface of the article to be plated with an exceedingly attenuated amalgam having the qualities which adapt it to the recep ion of metals by electrodeposition. The

processes which seek to prepare the surface of aluminium by the usual methods of subjecting the metal to striking solutions or whiteners are faulty, for there is not a perfect union between the metal deposited and the surface receiving it, as demonstrated by the formation some time after plating of the salts above referred to between the surface of the article plated and the metal film deposited thereon, caused by the attack of the solutions upon certain impurities in the aluminium and which in time result in the formation of a metallic salt, as stated.

The striking solutions or whiteners should, preferably, for general work, be three in number and graduated as to richness in metal and operated with electric currents of varying intensity aud quantity, and they are substantially such as are used for fixing a metallic base on other metals than aluminium whereon to make the final deposition of the metal desired.

The striking solutions which have been found to produce the best results are composed as follows and are three in number, and the electric current best suited to their proper operation is herein indicated:

Solution No. 1 is composed of ten penny- Weights of chlorid of silver and three pounds of cyanid of potassium to one gallon of rainwater, to which is added four ounces of water ammonia. The usual anode of silver of suitable fineness and size is hung on the rod connected with the positive pole of the battery or dynamo and a piece of copper in the solution on the opposite side of the tub, the copper serving to take up any excess of silver or other metal in the solution when the object being plated is hung in the solution. It is well known that to obtain the proper results in the electrodeposition of metals the strength of the electric current should bear a certain relation to the amount of exposed metal surface in the plating-bath. In striking solutions which contain but a small amount of metal in solution and'which should be deposited on the article to be plated in an exceedingly thin coating, the exposure in said bath of an article having a small exposed surface and without a reduction of the current proportionate to said surface will result in the too-rapid precipitation of the metal toward the said article and result in imperfect work. As it is practically impossible to prop erly graduate the electric current to adapt it to the constantly-increasing surface of metal exposed in the whitener as the articles are one after another hung in the solution, it is customary to hang in said whitening solution the piece of copper above referred to, which chemically diverts a part of the silver to itself and prevents overdeposition on the articles on the negative rod. As soon as the vat has been filled, or nearly filled, the copper is withdrawn from the solution, as owing to the increased area of the exposed surface on the negative rod there will be no danger of the too-rapid deposition of metal thereon. The proper current for this solution is one of substantially four and one-half volts and of fifteen amperes.

Solution No. 2 is composed of twelve pennyweights of chlorid of silver and three pounds of cyanid of potassium to one gallon of rainwater. Two anodes of silver are used in this solution on the positive rods and one on each side of the object to be plated. The current for this solution is the same as for No. 1.

Solution No. 3 is composedof one pound of aqua-ammonia and one pound of cyanid of potassium, twenty ounces of carbonate of copper, and one ounce of carbonate of zinc to one gallon of rain-water. This solution should have a gravity of about 12 by Baum hydrometer, and in operating it two brass anodes are used and the current is changed to three volts and twenty-five amperes. This solution can be worked as a brass or bronze solution.

From the whiteners or striking solutions the article may be plated with any desired metal in the usual manner.

Of course the articles must be thoroughly rinsed when taken out of No. 2 solution before putting them into No. 3, as the component parts of the latter would suffer deterioration through contact with the former.

Having thus described my invention, what I claim, and desire to secure by Letters Patent of the United States, is-

1. The method of treating aluminium and its alloys preparatory to the electrodeposition of the final coating thereon, consisting of the successive immersion in solutions as follows: muriatic acid, cyanid of potassium, phosphoric acid, and thence into a solution containing a mercurial salt, whereby the surface of the aluminium has fixed thereon an amalgam of mercury before being immersed in an electrically-operated solution, substantially as described.

2. The process of electrically depositing metals on aluminium and its alloys consisting in cleaning the surface thereof, then dipping it, first, in a muriatic-acid solution having a gravity of substantially 15 Baum;

second, in a cyanid-of-potassium solution having a gravity of substantially 20 Baum; third, in a phosphoric-acid solution having a gravity of substantially Baum; fourth, in a solution containing bichlorid of mercury, and, fifth, then into an alkaline solution; sixth, passing it through suitable electricallyoperated striking solutions, and from thence, seventh, into the electrically-operated solutions for depositing thereon the final coating of metal, substantially as described.

3. The process of plating aluminium comprising the following steps, after suitably cleansing it, by dipping it in a suitable alkali, as a solution of whale-oil soap, first, dipping in muriatic-acid solution havinga gravity of substantially 15 Baum; second, dipping in cyanid-of-potassium solution having a gravity of substantially 20 Baum; third, dipping in a phosphoric-acid solution having a gravity of substantially 50 Baum; fourth, dipping in a solution comprising one gallon of water, two pounds of either sal-ammoniac or muriate of ammonia, and one ounce of bichlorid of mercury; then, fifth, dipping in an alkaline solution, as caustic potash; sixth, and thence through the electrically-connected whitening or striking solutions, and then, seventh, into the electrically-connected solutions containing the metal to be deposited, substantially as described.

I 4:. The method of preparing aluminium for the deposition of the final metallic coating thereon, consisting in chemically cleansing the surface thereof substantially as described, applying an amalgam of mercury to said surface, then passing the metal successively through baths containing in solution the metal to be deposited thereon as a primary coating, which solution is operated by currents of progressivelyincreasing strength and are progressively graded as to the amount of metal in solution therein, substantially as described.

WILLIAM H. LEGATEi Witnesses:

EDWARD L. STEELE, JORDAN G. WELLS. 

